<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"> 
<title>CSS基本语法</title> 
<style>
.border-red{
    border:10px solid red;
}
.border-red .border-blue{
    border:10px solid blue;
}
.rel{
    position: relative;
    display: inline-block;
}
.abs{
    position: absolute;
    width:120px;
}

</style>
</head>
<body>
    <div class="border-red rel">
        lfkjsdlf555555555555555555555555j
        <span class="border-blue abs">文本</span>
    </div>
</body>
</html>